diff --git a/src/k1link/simulation/gaussian_pipeline_gateway.py b/src/k1link/simulation/gaussian_pipeline_gateway.py
index fe2b78c..5aa98f2 100644
--- a/src/k1link/simulation/gaussian_pipeline_gateway.py
+++ b/src/k1link/simulation/gaussian_pipeline_gateway.py
@@ -36,6 +36,7 @@ IMAGE_DIGEST_PATTERN: Final = re.compile(r"^sha256:[a-f0-9]{64}$")
 DEFAULT_CHUNK_BYTES: Final = 8 * 1024 * 1024
 MAX_JSON_RESPONSE_BYTES: Final = 32 * 1024 * 1024
 MAX_RETRIES: Final = 3
+RETRYABLE_PROVIDER_STATUS_CODES: Final = {502, 503, 504}
 DEFAULT_INGEST_TIMEOUT_SECONDS: Final = 30 * 60.0
 
 
@@ -899,7 +900,10 @@ def _validate_runtime_provenance(document: Mapping[str, object]) -> None:
 
 
 def _unavailable(message: str, error: httpx.HTTPError) -> GaussianPipelineGatewayError:
-    if isinstance(error, httpx.TransportError):
+    if isinstance(error, httpx.TransportError) or (
+        isinstance(error, httpx.HTTPStatusError)
+        and error.response.status_code in RETRYABLE_PROVIDER_STATUS_CODES
+    ):
         return GaussianPipelineUnavailableError(message)
     return GaussianPipelineGatewayError(message)
 
@@ -922,4 +926,6 @@ def _provider_rejection(response: httpx.Response) -> GaussianPipelineGatewayErro
     message = f"Gaussian provider rejected request (HTTP {response.status_code})"
     if detail is not None:
         message = f"{message}: {detail}"
+    if response.status_code in RETRYABLE_PROVIDER_STATUS_CODES:
+        return GaussianPipelineUnavailableError(message)
     return GaussianPipelineGatewayError(message)
diff --git a/tests/test_gaussian_pipeline_gateway.py b/tests/test_gaussian_pipeline_gateway.py
index 1537e95..f1850e7 100644
--- a/tests/test_gaussian_pipeline_gateway.py
+++ b/tests/test_gaussian_pipeline_gateway.py
@@ -14,6 +14,7 @@ from k1link.simulation.gaussian_pipeline_gateway import (
     GaussianPipelineGateway,
     GaussianPipelineGatewayError,
     GaussianPipelineIntegrityError,
+    GaussianPipelineUnavailableError,
     _discover_bundle_members,
 )
 
@@ -256,6 +257,30 @@ def test_gateway_surfaces_bounded_provider_rejection_detail(tmp_path: Path) -> N
         ))
 
 
+@pytest.mark.parametrize("status_code", [502, 503, 504])
+def test_gateway_classifies_temporary_provider_proxy_failures_as_unavailable(
+    tmp_path: Path,
+    status_code: int,
+) -> None:
+    with (
+        GaussianPipelineGateway(
+            "http://gaussian.test",
+            _token_file(tmp_path),
+            transport=httpx.MockTransport(
+                lambda _request: httpx.Response(
+                    status_code,
+                    json={"error": "provider_unavailable"},
+                )
+            ),
+        ) as gateway,
+        pytest.raises(
+            GaussianPipelineUnavailableError,
+            match=rf"HTTP {status_code}.*provider_unavailable",
+        ),
+    ):
+        gateway.capabilities()
+
+
 def test_gateway_rejects_incomplete_lcc_bundle(tmp_path: Path) -> None:
     bundle = tmp_path / "bundle"
     bundle.mkdir()